Pressure vessels are utilized for many applications. These applications include self-contained breathing apparatuses, oxygen cylinders for medial and aircraft uses, fuel storage for alternative fuel vehicles, fire extinguishers, among others. Pressure vessels can be classified into one of four types: Type 1 is an all metal construction; Type 2 is a metal lined with fiber composite hoop wrap construction; Type 3 is a metal lined with a composite full wrap; and Type 4 is a plastic lined with composite full wrap.
A composite overwrapped pressure vessel (COPV) is a Type 4 vessel having a thin, non-structural liner wrapped with a structural fiber composite, designed to hold a fluid or gas under pressure. The liner provides a barrier between the fluid (e.g., gas) and the composite, preventing leaks (which can occur through composite matrix microcracks which do not cause structural failure) and chemical degradation of the structure. In general, a protective shell is applied for protective shielding against impact damage and as a primary structural element of the composite overwrapped pressure vessel. These composites can be fiber reinforced polymers (FRP), using carbon, fiberglass, and kevlar fibers. One advantage of a COPV as compared to a similar sized metallic pressure vessel is lower weight.
The vessel wall of a filament-reinforced plastic lined type IV pressure vessel or COPV is substantially continuous, and formed of a composite laminated structure. The inner portion or layer of the vessel wall is often a thermoplastic liner having an inner surface and an outer surface. The outer portion or layer of the vessel wall can be formed of overlapping helically-wound and hoop wound reinforcing filaments that are wet-wrapped with thermoset plastic and bonded to the outer surface of the thermoplastic liner.
As is the case with fluid-containment vessels, the aforementioned conventional thermoset and thermoplastic composite pressure vessels need at least one port, and frequently several ports, for providing access to fill and/or empty the vessel and/or for permitting the attachment of devices that monitor the pressure and/or other conditions within the interior of the vessel. These ports are commonly provided as rigid metallic fittings that are adapted to connect to hoses, pipes and/or measurement equipment (e.g., pressure sensors and gauges).
Unfortunately, bonding the rigid metallic port to the thermoplastic composite pressure vessels has proven to be difficult. It is commonly believed that, unless the port structure is bonded to the thermoplastic liner and the thermoset and filament reinforced outer layer, the mechanical strength of the pressure vessel is substantially weakened. Moreover, in conventional vessels, severing the continuous filament reinforcement can undermine the strength of the vessel.
Therefore, there exists a need in the art for an improved composite pressure vessel, and for a method for forming a port in a wall thereof. There further exists a need in the art for a fitting assembly that is adapted to be efficiently secured to the pressure vessel so as to define a port therein.